Question

An influent waste-water stream contains \(330 \mathrm{mg} \mathrm{L}^{-1}\) organic matter (both suspended and soluble) and \(27 \mathrm{mg} \mathrm{L}^{-1}\) ammonium ion (as \(\mathrm{N}\) ). Calculate the total BOD. What assumptions is it necessary to make?

Short answer

Total BOD is 453.39 mg/L. Assumptions include standard consumption values and no additional BOD sources.

Step-by-step solution

Understanding Biochemical Oxygen Demand (BOD)

Biochemical Oxygen Demand (BOD) is a measure of the amount of organic material in water that can be biologically oxidized. It is an important parameter for assessing water pollution.

Total BOD Calculation

To calculate total BOD, you need to find the sum of carbonaceous BOD (CBOD) and nitrogenous BOD (NBOD). CBOD is calculated based on organic matter content, while NBOD is calculated from the ammonium ion content.

Calculate Carbonaceous BOD (CBOD)

Assume 1 mg of organic matter consumes 1 mg of oxygen for its degradation. Therefore, CBOD = 330 mg/L.

Calculate Nitrogenous BOD (NBOD)

NBOD can be estimated by assuming approximately 4.57 mg of oxygen is required to oxidize 1 mg of ammonium nitrogen. Therefore, NBOD = 27 mg/L * 4.57 mg O2/mg N = 123.39 mg/L.

Total BOD Calculation

Add CBOD and NBOD to obtain total BOD: Total BOD = CBOD + NBOD = 330 mg/L + 123.39 mg/L = 453.39 mg/L.

Assumptions Made

The main assumptions are: (1) all organic matter contributes to CBOD, (2) the conversion factor of 4.57 mg O2/mg N for NBOD is accurate, and (3) there are no additional substances in the water stream contributing to BOD.

Key concepts

Water Pollution Assessment

Water pollution assessment is crucial in understanding and managing the health of aquatic ecosystems. It involves evaluating various parameters, including Biochemical Oxygen Demand (BOD), to determine the level of pollution in a water body.
BOD is a key indicator used to assess the presence of organic pollutants in water. High BOD values often indicate a high concentration of biodegradable organic material, which can lead to oxygen depletion in aquatic environments.

• When BOD levels are high, it suggests that there is a significant amount of organic matter that microorganisms can consume, leading to a decrease in oxygen.
• This depletion of oxygen can harm aquatic life, affecting fish and other organisms that rely on oxygenated water.
• By measuring BOD, environmental scientists can gauge the pollution levels and determine necessary remediation efforts.

Regular monitoring and understanding BOD are essential for preserving water quality and ensuring the sustainability of aquatic ecosystems.

Organic Matter Oxidation

Organic matter oxidation is a critical process that affects water quality. It involves the breakdown of organic materials by microorganisms, which use oxygen during this process.
In the context of water bodies, this consumption of oxygen can significantly impact BOD levels.

• Microorganisms decompose organic matter, such as plant debris and animal waste, using oxygen in the process, which results in the chemical reduction of organic compounds to simpler substances.
• This oxidative process releases energy that microorganisms harness to grow and reproduce.
• The rate of oxidation and the amount of oxygen required depend on the type and quantity of organic matter present.

Understanding organic matter oxidation is essential because it directly influences the calculation of Carbonaceous BOD (CBOD), which is the part of BOD associated with carbonaceous organic matter. Elevated levels of CBOD indicate a higher demand for oxygen, which can lead to environmental issues such as hypoxia in water bodies.

Nitrogenous BOD Calculation

Calculating nitrogenous BOD (NBOD) is another vital step in evaluating BOD and understanding the broader impact of pollutants in a water system.
Unlike carbonaceous BOD, NBOD specifically deals with the oxidation of nitrogenous compounds, primarily ammonium ions.

• The calculation of NBOD is done by estimating the oxygen required to convert ammonium (\(\text{NH}_4^+\)) into nitrate (\(\text{NO}_3^-\)), which involves complex biochemical reactions that are mediated by specific bacteria.
• The process is often simplified by using conversion factors; for instance, it is generally assumed that 4.57 mg of oxygen is needed to oxidize 1 mg of ammonium nitrogen.
• In the earlier problem solution, the NBOD was calculated using this conversion factor, resulting in a value of 123.39 mg/L.

This calculation is crucial for accurately determining the total BOD and assessing the potential ecological impact of nitrogen-rich waste on aquatic life.

Environmental Chemistry

Environmental chemistry plays a pivotal role in understanding the chemical processes and compounds that affect natural water bodies. It provides insights into the composition, reactions, and transformations of substances in the environment.

• In environmental chemistry, scientists investigate how pollutants, such as organic and nitrogenous wastes, interact in ecosystems and affect environmental health.
• Understanding these interactions helps in predicting the behavior of pollutants and their potential impacts on ecosystems.
• Through analyzing chemical processes like oxidation, environmental chemistry enables the development of strategies for pollution control and remediation.

In the context of BOD, environmental chemistry aids in clarifying the mechanisms involved in organic matter and nitrogenous compound degradation. It helps develop more accurate methods for assessing water pollution, contributing to more effective environmental management and protection strategies.